The files markdown/preamble/version-history.md and
markdown/specification/scoring-metrics-glyph-registration.md
had some stray <span> elements that didn't appear
to be doing anything.
Also updated the generated gitbook files.
Thanks to @bhamblok for the report.

…24-25-26-27-28-29-30-31-32-33-34-35-36-42-43-44-48-49-51-smufl-1.2
This pull request constitutes all of the material changes required to address the specified additions and changes for SMuFL version 1.2. The remaining task is to finalise the release, subject to community approval, and in the process adopt the W3C FSA license (#38).